From: GOLBERY Irčne (irene.golbery@xxxxxxxx)
Date: Wed Apr 24 2002 - 16:26:01 GMT-3
Sorry for the previous mail.
This Mail is in .txt format then now readable.
OK for the "clear ip bgp *" after all changes.
In fact when readable in the "show ip bgp" command you will see that the
0.0.0.0 is because of the network 199.105.176.0 is genarated by the router
itself(sorry again) see "sh ip bgp" entries R1, R2 and R3.
R1 configuration :
router bgp 64513
bgp default local-preference 200
network 199.105.176.0 mask 255.255.248.0
!
ip route 199.105.176.0 255.255.248.0 Null0
-----------
R2 configuration:
router bgp 64513
bgp default local-preference 150
network 199.105.176.0 mask 255.255.248.0
!
ip route 199.105.176.0 255.255.248.0 Null0
----------
R3 configuration:
router bgp 64513
network 199.105.176.0 mask 255.255.248.0
!
ip route 199.105.176.0 255.255.248.0 Null0
-----------
R4 configuration:
router bgp 64513
neighbor 3.3.3.3 remote-as 64513
neighbor 3.3.3.8 remote-as 64513
neighbor 3.3.3.9 remote-as 64513
Thanks a lot Howard for all the sources of information you gave me.
"Is there a problem you are trying to solve? "
--> Yes or not exactly
--> probably not so interesting...
In fact I just want to be shure that the test I have done works properly
and then it's the reason why I am searching for How does the + show ip bgp
;
command interpret the information of the local preference
Details :
R1(lo0:3.3.3.9), R2(lo0:3.3.3.8),R3(lo0:3.3.3.3) and R4(lo0:3.3.3.1) are
full mesh iBGP peers in AS 64513
R1, R2 and R3 have :
- an ip route : ip route 199.105.176.0 255.255.255.248 null0
- and the network command : network 199.105.176.0 mask 255.255.248.0
R1 default localpref is 200
R2 default localpref is 150
R3 default localpref is 100 (the default)
I'm guessing a bit because I don't see your full configuration. But I notice
that all the routers except R4 have a default route with a maximum weight.
First, have you tried clear ip bgp * after each change?
Second, have you tried this without defaults?
This is the result of the + SHOW IP BGP ; COMMAND
Remarks:
Look at R4, it sees all the routers announcing the network 199.105.176.0/21
even the one with the local preference of 100
Look at R1 , it represents only the network announced by a peer of which the
localpref is different than 100
R1#sh ip bgp
Network Next Hop Metric LocPrf Weight Path
* i199.105.176.0/21 3.3.3.8 0 150 0
i
*> 0.0.0.0 0 32768
i
R2#sh ip bgp
Network Next Hop Metric LocPrf Weight Path
* i199.105.176.0/21 3.3.3.9 0 200 0
i
*> 0.0.0.0 0 32768
i
R3#sh ip bgp
Network Next Hop Metric LocPrf Weight Path
* i199.105.176.0/21 3.3.3.8 0 150 0
i
* i 3.3.3.9 0 200 0
i
*> 0.0.0.0 0 32768
i
R4#sh ip bgp
Network Next Hop Metric LocPrf Weight Path
* i199.105.176.0/21 3.3.3.3 0 100 0
i
*>i 3.3.3.9 0 200 0
i
* i 3.3.3.8 0 150 0
i
Connectivity works, I just want to be sure that the result of the + show ip
bgp ; command of all the routers is OK.
Sincerely,
Irene.
-----Message d'origine-----
De : Howard C. Berkowitz [mailto:hcb@gettcomm.com]
Envoyi : mercredi 24 avril 2002 13:37
@ : 'ccielab@groupstudy.com'
Objet : Re: TR: BGP and Local Preference
At 11:33 AM +0200 4/24/02, GOLBERY Irhne wrote:
Thanks Yakout,
Your are explained me what I am able to read and understand in the trace I
sent to you.
But my question is very precise.
I am looking for a documentation where it is explained in details
Irhne.
Is there a problem you are trying to solve?
What additional detail are you looking for?
1. How it is formatted in the BGP Update message?
See RFC1771, or, probably more accurately, the latest revision draft,
http://www.ietf.org/internet-drafts/draft-ietf-idr-bgp4-17.txt It is
a 16 bit integer attribute of AS-wide scope, which means it will only
be seen in iBGP (although there are some implementations that send it
externally, this is nonstandard. MED is meant for that purpose)>
2. How it is used in the BGP route selection algorithm?
Look in the archives or my WAN Survival Guide book; I've written it
up several times. You can also go to www.nanog.org, and search for
the BGP tutorials by Avi Friedman, Paul Ferguson, and myself?
3. What is its purpose, in the sense of how it is used in real life?
You'll find some of that in the tutorials above. Halabi touches on
it lightly. You can read about preference in the various Routing
Policy Specification Language documents and then see the applicability
of a preference of AS-wide scope. I discuss some detailed applications
in my Building Service Provider Networks book, but that won't be
available until June. I've also posted some applications in the
archives.
-----Message d'origine-----
De : yakout esmat [mailto:yesmat@iprimus.com.au]
Envoyi : mercredi 24 avril 2002 11:01
@ : GOLBERY Irhne; ccielab@groupstudy.com
Objet : RE: BGP and Local Preference
Irene,
Easy, Local Pref is a value given to routes as they enter the AS and stay
with these routes as they propagate within this AS.
In your example:
1) Route 10.0.0.0 is assigned LocalPref of 200 as it enters AS1 by RA. it
shows in your output 'show ip bgp'.
2) Router A passes the route to RB with the same value, so it also shows in
'show ip bgp'in RB.
If you haven't changed the localpref value for the route (10.0.0.0) coming
from RC as you did, it would have had the default which is 100.
Rule: You will only see a value (100 or otherwise) next to local routes
only
learned through IBGP.
Since Localpref value doesn't travel with the route outside the AS, you
will
see this value empty next to routes learned through EBGP as you have in
your
output.
HTH
Ya
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
GOLBERY Irhne
Sent: Wednesday, April 24, 2002 6:03 PM
To: ccielab@groupstudy.com
Subject: BGP and Local Preference
Hello,
I am looking for some URL or documentation + EXPLAINING IN DETAILS + how
does local preference is represented in the SHOW IP BGP command ?
10.0.0.0/8
RC (AS 2) RD
RA (AS 1) RB
I mean,
* RA(lo0:3.3.3.1) iBGP peer with RB (lo0:3.3.3.2) in AS 1
* RA(lo0:3.3.3.1) eBGP peer with RC (lo0:3.3.3.3) in AS 2
* RB(lo0:3.3.3.2) eBGP peer with RD(lo0:3.3.3.4) in AS 2
RA set a Local preference of 200 for network 10. 0.0.0 announced by RC
RB doesn 't change the defaul local preference
When looking at the sh ip bgp,
RB#sh ip bgp
Network Next Hop Metric LocPrf Weight
Path
* 10.0.0.0/8 3.3.3.4 0 2 i
*>i 3.3.3.1 200 0 2 i
RA#sh ip bgp
Network Next Hop Metric LocPrf
Weight Path
*> 10.0.0.0/8 3.3.3.3 200 0 2 i
How does the + show ip bgp command + interpret the information of the
local
preference ?
I need to find details informations.
Thanks for your help
Irene.
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:58:18 GMT-3